ihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA MLKJIHGFEDCBA IndianJournal of Pure & Applied Physics Vol. 45, January 2007, pp. 75-78 / Ab-initio calculation and B 1 to B2 structural phase transformation in CdO at high pressure Vipul Srivastava, Sankar P Sanyal & M RajagopaJan* Department of Physics, Barkatullah University, Bhopal 462 026 *Department of Physics, Anna University, Chennai 600025 Received 1 March 2006 ;accepted 9 October 2006 The electronic and structural properties of CdO at high pressure have been studied by using the self-consistent tight binding linear muffin tin orbital method. The relative stabilities of CdO at high pressure in the rock salt and CsCl structures have been examined. The rock-salt structure is found to be the ground state structure of CdO. The phase transition from NaCl (BI)- to CsCl (B 2 )-type structure for CdO is found to occur at 81.7 GPa, which is close to experimental value 90.6 OPa. Calculated lattice parameter and bulk modulus in both the phases are in good agreement with experimental results. The calculated band structure shows a small overlap between the conduction and valence bands with a direct band-gap of -1.37 eV. A broadening of the upper Cd-4d and 0-2p bands with some intermixing between them is observed in total DOS histogram of CdO. Keywords: Ab-initio calculation, Structural phase transformation, CdO, High pressure, Band structure IPC Code: HOIL, B30B 1Introduction The group lIB-VIA semiconductors have been extensively studied because of their technological importance. A number of interesting transition-metal oxides'" (TMO), such as FeO, MnO, CoO, NiO and ZnOattracted the attention of physicist to investigate the equilibrium and high pressure crystallographic structure and their stability. Some of them. ,~how striking features, like band-overlap metallization phenomenon under pressure, localization of their d- electrons due to a combination of strong electron- electron correlation energies and narrow d-electronic bands I. One might, therefore, consider the partially filled nature of the d-electronic shells in these compounds to explain metallic and insulator behaviour. In CdO, extensive experimental and theoretical studies on structural and electronic properties at high pressure are reported. Drickamer" and Zhang' could notobserve any structural phase transformation up to 8 GPa. Further, Guerrero-Meren0 6 from the first principle total energy calculations found that the rock saltstructure was the stable phase of CdO at ambient pressure and high pressure phase was cesium chloride, which has been calculated at pressure of .E-mail: spsanyal@sancharnet.in about 89 GPa. An additional second local minimum of energy in the wurtzite structure has also been reported. In band diagram of CdO in NaCI phase, a small overlap between the conduction and valence bands of -0.5 eV and a direct band gap of -0.7 eV have been calculated. The hybridization in Cd-dd and 0-2p states was also found during NaCI -? CsCI-type structural phase transition. On the other hand, Liu 7 performed experimental study on the compressibility and phase transition of CdO up to 176 GPa using high-resolution angular-dispersive X-ray diffraction (ADXD) technique. NaCI- to CsCI-type structural phase transformation was observed for CdO at a pressure of 90.6 GPa, with a bulk modulus as 147 and 169 GPa, respectively for the two phases. In the present paper, the electronic and structural properties of CdO using tight binding linear muffin tin orbital (TB-LMTO) method have been investigated. The electronic band structure, density of states and high pressure structural phase stability of CdO compound have been calculated and compared with the available experimental data and other theoretical results. We have found NaCI- to CsCl-type structural phase transformation in CdO at 81.7 GPa. The calculated lattice parameters and bulk mudulii in both the phases have been compared with the experimental findings. The results of the present study